This invention relates to a magnetic levitation system.
For many applications a rigid body needs to be suspended while frictionless motion in at least one degree of freedom must be allowed without are storing force. The gravitational force acting on the body must be exactly compensated independent of the body's position. Examples: seismometer, inclinometer.
Many scientific instruments measure a force experienced by a mass. Examples: accelerometer, balance. One method to measure such a force is to convert the force as precisely as possible to an electrical signal like a voltage or a current that can be measured with digital meters.
Sometimes, a levitating body not only needs to be isolated from external forces but also must be housed in a closed vessel. This is for example the case, when the reaction of an aggressive gas with a sample material is studied using a balance to measure the mass of the reaction products. In such a case no sensitive mechanical or electronic parts can be placed inside the reaction vessel.
Mechanical suspension systems, utilizing pin or edge bearings, torsion wires, leaf springs, or the like, cause internal friction and forces being a function of position. Active magnetic bearings are bound up with strongly position dependent forces and need electric power, a disadvantage for mobile instruments. Passive magnetic bearings by means of superconductors are ideal in terms of low friction and are used successfully, e.g. for gravimeters. But the expense for cooling the superconductors is considerable.
A force to be measured can be converted to the extension or contraction of a spring. This method is based on the assumption of the spring constant being really constant. A piezoelectric sensor or any field of force with a constant gradient can be regarded as a <<spring>> in a wider sense. Such fields of force can for example be related to electric or magnetic fields acting on electric charges, magnetic dipoles, or a current carried by a conductor. A good alternative to the <<spring>> is given by a closed-loop servo system consisting of a position sensor, an amplifier, and an actuator holding the movable part in place by exactly compensating the force to be measured. The force output of the actuator corresponds to an electrical variable representing the force to be measured. Examples: the currents carried by either the rotating coil of a galvanometer or the moving coil of a voice-coil drive. The currents must be supplied to these coils by flexible leads or sliding contacts causing interfering forces and friction.
A sample in a closed vessel can be weighed with a so-called magnetic-suspension balance. A magnetic-suspension balance is simply a conventional balance carrying an electromagnet outside of the vessel. The electromagnet, controlled by a position transducer, is carrying the sample inside the vessel. The electromagnet acts as a tare weight and needs current leads responsible for additional forces disturbing the balance.